For more than a century, scientists have debated whether intelligence is mostly a product of nature or nurture. Identical ...

Identical twins who were raised apart may have IQ differences similar to those of total strangers, according to new research.

In 2004, Michigan police found that DNA recovered from a crime scene matched that of Jerome Cooper, a notorious criminal. But what seemed like an open-and-shut case got complicated when the cops found ...

From Romulus and Remus—the myth of the twin brothers who founded the city of Rome—to the synchronized speech of Australia's "Twinnies" Paula and Brigette Powers, identical siblings have long inspired ...

The mom was 20 weeks pregnant when she discovered that her twins, Graylen and Chaysen, had twin-to-twin transfusion syndrome.